This invention relates to optical systems of ophthalmoscopic cameras for observation and photography of the fundus of an eye, and more particularly to a novel optical construction for separating a bundle of illuminating light rays from image-forming rays prior to entering a photographic relay lens, while shielding reflections occurring on the front and rear surfaces of an objective lens adapted to illuminate the fundus of the eye.
The conventional ophthalmoscopic cameras, as, for example, disclosed in British Pat. No. 799,812, generally employ a ring-shaped bundle of illuminating light rays projected onto the cornea of an eye to be examined, so that the rays reflected from the ocular fundus and emerging from the central portion of the cornea produce an image of the ocular fundus at the film plane after having passed through a central hole of an illuminating mirror positioned between an objective lens and a photographic relay lens. This apertured mirror is designed to be suitable for assisting in formation of an image of a ring-shaped slit of the illuminating arrangement without introducing into the image-forming rays disturbing undesirable light due to the reflections on the cornea.
Another source of disturbing reflections of illuminating rays is the surfaces of the objective lens. In order to eliminate such a disadvantage, one solution has been proposed in U.S. Pat. No. 3,594,071. According to this proposal, that portion of the illuminating light which would be subject to reflection from the objective lens surfaces is previously shielded by a small black dot provided on the optical axis in the illuminating optical system.